Inverted E. coli vesicles and a variety of proteoliposome preparations were evaluated for reconstitution of bacteriorhodopsin (BR) to form a light-driven system to build and maintain high levels of delta muH+. The system chosen involves reversed phase evaporation of a suspension of purified phospholipids in an ether water mixture. Improved optics and electronics are under development to quantify the extents of Ph and electrical gradients that are formed. The system will be used to measure the quantum efficiency of proton pumping in low and high steady state levels of illumination and to probe the roles of deltapH and delta psi in the energetics of ATP synthesis and hydrolysis under catalysis of the membrane-bound ATP synthase, FoF1.